A little embarrassing, but in the end it was definitely worth it.
When I was 17, my family went to Greece with our good family friends to stay in a villa. I was an only child, as was my family friend's daughter, Meghan. She was super attractive, about 5-6 with a great body, but we had never really had any flirting, mostly because I always saw her with my whole family and we never spent much time alone. However in the first week of our Greek vacation, it became apparent that the parents were going to go off to do their own thing, and me and Meghan got to spend a lot of time together. We started to have a really good chemistry, lots of teasing and casual flirting.
One day we went into the nearby village and found a nice beach to sit at. We were both sitting on a towel together, her in a bikini and me in board shorts, when a couple gets out of the water, the girl topless and the guy in a tight bathing suit above his knees. We hadn't really talked about anything sexual, and both of us fell silent, even though we shouldn't have been so surprised, as topless was the custom in Europe. After a couple minutes of awkward giggling and jokes, I made a comment to the order of 'you don't want to look to touristy, I think you might have to do what she did just to fit in.' To my surprise, instead of slapping me, she said tomorrow she would, but on one condition: she got to pick out my bathing suit, and I would have to put it on at the villa and walk through town to the beach. I immediately agreed, figuring that the bathing suit she picked would be something like the one we just saw, short and tight but not too revealing, and knowing that a lot of people wore their bathing suits in town I wasn't too worried.
The next morning, after our parents left, she came into my room with my new suit. Not only was it not board shorts, it wasn't the tight bathing suit I expected; It was a tiny speedo. She told me to put it on, and I started to go to the bathroom, but she told me that if I was going to be so shy she would be as well. She had an amazing chest, and I definitely didn't want that, so I turned around, slipped off my pants and put on the speedo, giving her just a view of my butt. She gave me a wink, grabbed a towel and we started on our way. Walking through town was the most embarrasing thing I've ever done. This speedo was smaller than the smallest pair of briefs, and my flaccid dick was straining against the nylon. She kept giving me little brushes against my thighs, and by the time I got to the beach I was hard as a rock, and there was nothing left to the imagination. As soon as we got there, I demanded she go topless, and she obliged, taking off her top with confidence. I nearly came in my pants she was so amazing, and she smiled at the results of her new suit, my hard dick clearly visible. She took out some sunscreen and told me I better put it on, I wouldnt want to be burned ALL over. I refused, jokingly, and she said fine, I'll put it on for you. She flipped me onto my back and started massaging it into my back, moving down to my legs, just barely reaching under the fabric and getting the top of my rear. Finally she told me to flip over. She started at my chest, moving past my abs, skipping my crotch and going to the legs. She moved her way up, then slowly slipped her lotioned hand under my speedo, moving her hand up my dick faster and faster. I couldn't help it, I came all over the suit and her hand, and she smiled and said I guess that's coming off now. The rest of the day was spent in a similar manner, I'll tell you about that soon.